1. Field of the Invention
The present invention relates to a valve timing controller for an internal combustion engine and, more particularly, to a valve timing controller for controlling the timing of operation of the intake valves and the exhaust valves of an internal combustion engine.
2. Description of the Related Art
In an internal combustion engine, the required valve timing for air intake and exhaust is varied according to the operating conditions. In the past, almost every internal combustion engine has a camshaft that is driven by a crankshaft via a timing belt or the like. The timing at which the intake and exhaust valves are opened and closed is fixed regardless of the angular position of the crankshaft. In recent years, however, variable valve timing systems have been adopted to improve the output of the internal combustion engine and to provide higher fuel economy and lower emissions. Accordingly, various techniques regarding valve timing have been disclosed.
One of these techniques is disclosed in Japanese patent laid-open No. 256878/1997. In this disclosed technique, the phase of the rotating output shaft of an internal combustion engine is displaced to drive a camshaft. Valve timing of at least one of intake and exhaust valves is adjusted. The valve timing is detected from the phase difference between the output shaft of the engine and the camshaft. Target valve timing is established from the operating conditions of the engine. The control gain of a valve timing-adjusting means is so set that the detected timing agrees in phase with the target valve timing. The displacement speed of the phase of the rotating camshaft is found from the transition of the actual valve timing. The displacement speed of this phase of rotation is compared with a reference value. The control gain is corrected such that the speed difference between them is reduced down to zero. In this way, displacement speed variations are absorbed. Response and convergence are improved.
More specifically, during adjustment of the valve timing, if the actual valve timing deviates from the target valve timing, a proportional value is created from the deviation. Based on this proportional value and on a derivative value calculated from this deviation, a duty factor for compensating the response delay is sent to an oil pressure control valve. Subsequently, a proportional value and a derivative value are similarly found from the deviation at some instant of time and thus another duty factor is found and sent to the oil pressure control valve. The duty factor is maintained until the deviation of the actual valve timing from the target valve timing becomes less than a given value. While this duty factor is being maintained, the variation in the actual valve timing between two points is found. Also, the time in which this variation occurs is found. The displacement speed of the phase of rotation is found from the variation and the time. This displacement speed is compared with a reference speed value. If the displacement speed is higher than the reference value, the duty factor for compensation of the response delay is set to a smaller value. If it is lower, the duty factor for compensation of the response delay is set to a larger value.
Japanese patent laid-open No. 217609/1997 discloses a technique for accurately controlling valve timing using a valve timing control mechanism that rotates relative to any one of the output shaft of an internal combustion engine and a camshaft driven by the output shaft within a given angular range. The valve timing control mechanism is operated according to the difference between the actual value of the angular distance between the output shaft and the camshaft and a target value. The angular distance is so controlled as to agree with the target value. If the deviation of the actually measured value from the target value does not vary, a correcting value for the valve timing control mechanism is so set as to reduce the deviation. In this way, valve timing can be accurately controlled without being affected by manufacturing tolerances.
Conventional valve timing controllers for internal combustion engine are constructed in this way. Of these conventional valve timing controllers s in the technique disclosed, for example, in the above-cited Japanese patent laid-open No. 256878/1997, a duty factor found at some instant of time is sent to an oil pressure control valve and maintained to detect the displacement speed of the phase of rotation. Where the deviation of the actual valve timing from target valve timing is found at regular intervals of time, if a proportional value and a derivative value are found from the deviation, and if control is provided using a duty factor found from these proportional value and derivative value, then responsiveness may deteriorate. Also, the detected displacement speed of the phase of rotation is compared with a reference value. The duty factor is corrected according to the difference. Consequently, only the initial response delay that produces a difference between the actual valve timing and the target valve timing is corrected. It cannot be said that sufficient correction is made. Hence, sufficient responsiveness may not be obtained.
The present invention has been made to solve the foregoing problems.
It is an object of the present invention to provide a valve timing controller which is for use with an internal combustion engine and which makes a correction adapted for the characteristics of the actually mounted oil pressure control valve to provide stable response in spite of variations in flow rate characteristics due to manufacturing tolerances, the valve timing controller being further characterized in that it can compensate for variations in flow rate characteristics by a control operation.
A valve timing controller built in accordance with the present invention and for use with an internal combustion engine having a crankshaft comprises: an intake cam driven by the crankshaft of the engine and acting to open and close intake valves; an exhaust cam driven by the crankshaft of the engine and acting to open and close exhaust valves; a valve timing-varying means mounted in a rotation transfer path between said crankshaft and at least one cam selected from the intake cam and the exhaust cam to vary the phase of rotation of said one cam relative to the crankshaft; a driving means for driving the valve timing-varying means; and a control means for controlling an amount of control over the driving means. This control means detects a difference of the amount of control over the driving means to cause the valve timing-varying means to operate in a desired manner under different operating conditions of the internal combustion engine. The amount of control over the driving means is determined according to the difference of the amount of control.
In one feature of the invention, the difference of the amount of control under a different operating condition of the engine is detected when the difference between an actually operated amount of motion to vary the valve timing and a target amount of motion to vary the valve timing satisfies a given condition.
In another feature of the invention, the control means learns amounts of control under different operating conditions of the engine. The amount of control over the driving means is determined from a difference of this learned value.
In a still other feature of the invention, the control means stores plural characteristics of the driving means. One of the plural characteristics is selected according to the difference of the amount of control under a different operating condition of the engine. Thus, the amount of control over the driving means is determined.
In a yet additional feature of the invention, the control means selects a poor response characteristic or control value from plural characteristics or control values until the amount of control over the driving means is determined from the difference of the amount of control under a different operating condition of the engine. The selected characteristic or control value is used as an amount of control over the driving means.
In an additional feature of the invention, there are further provided detecting means for detecting the angular position of said one cam relative to the crankshaft and an arithmetic means for calculating target position of the angular position of said one cam relative to the angular position of the crankshaft according to the operating conditions of the engine. The control means performs proportional and derivative control operations according to the difference between the detected relative position and the target position and sets plural proportional and derivative control values. One of the proportional and derivative values is selected according to the difference of the amount of control under a different operating condition of the engine. Thus, the amount of control over the driving means is determined.
In a still other feature of the invention, there are further provided detecting means for detecting the angular position of said one cam relative to the crankshaft and an arithmetic means for calculating target position of the angular position of said one cam relative to the angular position of the crankshaft according to the operating conditions of the engine. The control means performs an integral operation according to the difference between the detected relative position and the target position and sets plural integral control values. One of the different integral control values is selected according to the difference of the amount of control under a different operating condition of the engine. Thus the amount of control over the driving means is determined.
In a still further feature of the invention, the control means stores plural different characteristics of the driving means. The control means interpolates one of the plural different characteristics according to the difference of the amount of control under a different operating condition of the engine. Thus, the amount of control over the driving means is calculated.
In a further additional feature of the invention, the amount of control over the driving means is calculated from each midway value obtained by interpolating the plural characteristics or control values until the amount of control over the driving means is set from the difference of the amount of control under a different operating condition of the engine.
In a yet other feature of the invention, there are provided a detecting means for detecting the angular position of said one cam relative to the angular positions of the crankshaft and an arithmetic means for calculating the target position of the angular position of said one cam relative to the crankshaft according to the operating condition of the internal combustion engine. The control means performs proportional and derivative control operations according to the difference between each detected relative position and the target position. The control means sets plural proportional and derivative value and interpolates one of the plural different characteristics according to the difference of the amount of control under a different operating condition of the engine. Thus, the amount of control over the driving means is calculated.
In a yet additional feature of the invention, there are further provided a detecting means for detecting the position of said one cam relative to the angular position of the crankshaft and an arithmetic means for calculating target position of the angular position of said one cam relative to the angular position of the crankshaft according to the operating conditions of the engine. The control means performs an integral control operation according to the difference between each detected relative position and the target position. The control means sets plural integral control values and interpolates one of the plural different integral control values according to the difference of the amount of control under a different operating condition of the engine. Thus, the amount of control over the driving means is calculated.
Other objects and features of the invention will appear in the course of the description thereof, which follows.